This research developed a mathematical model and optimization of materials for the development of metakaolin self-compacting concrete. This is in a bid to reduce the overall material quantity and cost towards sustainable infrastructural construction. To achieve the aim of this research, Response Surface Analysis (RSM) was used. Kaolinitic clay was De-hydroxylated at 750°C to form metakaolin. This was used as a partial replacement for cement at 0%, 5%, 10%, 15%, 20% and 25% weight of Portland limestone cement. Both strength and rheology properties of the developed metakaolin self-compacting concrete were assessed. To this end, slump flow, L-Box test and V-funnel test were carried out alongside the compressive strength using relevant standard. The result of the research revealed that at 15% addition of metakaolin the slump flow, passing ability and filling ability was unsatisfactory according to EFNARC standard. From the numerical optimization of the compressive strength, the maximum predicted compressive strength of 44.35 N/mm2 was obtained. At a low value of metakaolin addition (5–15%), the compressive strength increased as the age of the concrete increased from 3–150 days. The age with the optimum mechanical strength formation was 110 days with metakaolin addition of 52.73 kg. The result of this research provide a database for Engineers, Researchers and Construction workers on the optimum metakaolin required to achieve satisfactory mechanical strength in metakaolin self-compacting concrete.

1. 7
INTRODUCTION
Cement is one of the most commonly used
construction materials in the world and its price
has risen at an alarming rate over the last few
years. This high increase in the cost of cement
has led to a reduction in concrete construction
in underdeveloped and developing countries.
This calls for the incorporation of natural non-
expensive material as a substitute for cement.
Metakaolin is a naturally occurring material
with pozzolanic properties, capable of replac-
ing a certain percentage of cement when used in
production of self-compacting concrete (SCC).
Self-compacting concrete is a recent develop-
ment in the concrete construction industry. It is
asserted as being the way forward in concrete
production based on its numerous advantag-
es [Ouchi and Hibino 2000]. Focus on sustain-
ability in line with the application of self-com-
pacting concrete was done by [Tarun and Naik
2012; Grdić et al. 2008; Navid et al. 2016; He-
sami et al., 2016; Aggarwal et al., 2008; Oka-
mura and Ouchi 2003] to mention a few. The use
of cement alone as a binder in self-compacting
concrete leads to thermal crack. In an attempt to
reduce the incidence of the crack and reduce the
cost of SCC production, the use of metakaolin as
Response Surface Analysis of the Compressive Strength
of Self-Compacting Concrete Incorporating Metakaolin
Ayobami Busari1*
, Bamidele Dahunsi2
, Joseph Akinmusuru1
,
Tolulope Loto3
, Samuel Ajayi4
1
Department of Civil Engineering, Covenant University, Ogun State, Nigeria
2
Department of Civil Engineering, University of Ibadan, Oyo State, Nigeria
3
Department of Mechanical Engineering, Covenant University, Ogun State, Nigeria
4
Nigerian Building and Road Research Institute, Ota, Ogun State, Nigeria
* Corresponding author’s e-mail: ayobami.busari@covenantuniversity.edu.ng
ABSTRACT
This research developed a mathematical model and optimization of materials for the development of metakaolin
self-compacting concrete. This is in a bid to reduce the overall material quantity and cost towards sustainable
infrastructural construction. To achieve the aim of this research, Response Surface Analysis (RSM) was used.
Kaolinitic clay was De-hydroxylated at 750°C to form metakaolin. This was used as a partial replacement for
cement at 0%, 5%, 10%, 15%, 20% and 25% weight of Portland limestone cement. Both strength and rheology
properties of the developed metakaolin self-compacting concrete were assessed. To this end, slump flow, L-Box
test and V-funnel test were carried out alongside the compressive strength using relevant standard. The result of
the research revealed that at 15% addition of metakaolin the slump flow, passing ability and filling ability was
unsatisfactory according to EFNARC standard. From the numerical optimization of the compressive strength, the
maximum predicted compressive strength of 44.35 N/mm2
was obtained. At a low value of metakaolin addition
(5–15%), the compressive strength increased as the age of the concrete increased from 3–150 days. The age with
the optimum mechanical strength formation was 110 days with metakaolin addition of 52.73 kg. The result of this
research provide a database for Engineers, Researchers and Construction workers on the optimum metakaolin
required to achieve satisfactory mechanical strength in metakaolin self-compacting concrete.
Keywords. response surface analysis, metakaolin, self-compacting concrete, sustainable infrastructure.
Volume 13, Issue 2, June 2019, pages 7–13
https://doi.org/10.12913/22998624/105608
Advances in Science and Technology
Research Journal
Received: 2019.01.15
Revised: 2019.02.15
Accepted: 2019.03.15
Available online: 2019.05.01

2. Advances in Science and Technology Research Journal Vol. 13(2), 2019
8
a supplementary material was adopted based on
its unique properties.
Metakaolin is obtained when Kaolinitic clay
is heated to a temperature of 650–900 o
C. At this
temperature, an endothermic reaction takes place
to form metakoalin, according to Justice et al.
(2005). The reaction of this material with modi-
fied cement paste micro structure is similar to the
pozollanic properties of silica fumes, rice husk
ash, fly ash etc. [Shivram and Nagesh 2007]. In
line with the use of other cementitious material,
the use of metakaolin was found to form a good
combination in concrete production [Kamaruddin
1991, Sabir et al. 2001, Nabil 2006, Jiping andAl-
binas 2009, Jian-Tong and Zongjin 2002, Hemant
2011, Vejmelková et al. 2010, Badogiannis et al.
2004 and Arikan et al. 2001].
The use of this mineral material was found to
improve the durability, strength and cohesion of
concrete structures [Justice et al. 2005, Kong and
Orbison 1987]. Studies showed that the introduc-
tion of 20% of metakaolin improves the strength
of concrete (Shepur 2014). However, there is a
need to assess the optimum quantity of this mate-
rial needed in self-compacting concrete. To this
end, Response Surface Analysis Method (RSM)
was adopted in this study.
Response Surface Methodology (RSM) is a
collection of mathematical and statistical tech-
niques useful for the modelling and analysis of
problems in which a response of interest is influ-
enced by several variables [Myers and Montgom-
ery, 1995; Akinoso et al., 2011]. It is a powerful
tool used for the optimization of chemical reac-
tions or engineering processes.
This unique tool was used to assess the effect
of metakaolin and Self-Compacting Concrete in
concrete technology.
The aim of making concrete affordable and
improving green construction motivated this re-
search. RSM was used to provide a data base on
the optimum strength achievable using metaka-
olin in self-compacting concrete for engineers,
researchers and construction workers.
MATERIAL AND METHODS
Locally available Portland limestone cement
(rapid hardening cement) conforming to NIS
(2003) was used in the study. The metakaolin used
as a supplementary material was sourced from
south western Nigeria. The kaolin used for this
research was sourced from the same geographic
location as in the study of Ogundiran and Ikotun
(2016) and Labiran (2016). Scanning Electron
Microscopy was used in assessing the chemical
composition, surface structure and particleometry
of the metakaolin. The chemical composition of
the metakaolin and the cement used is as shown
in Table 1. Coarse and fine aggregate of size
4.5 mm and 19.5 mm were used in the research. A
polycarboxylate-based high-range water reducing
admixture (HRWRA), super-plasticizer was used
in this research according to EFNARC (2002).
Metakaolin was used as a replacement for the
Portland limestone cement at 0%, 5%, 10%, 15%,
20% percentage of the dry weight of the cement.
The total paste volume was kept constant for all
SCC mixtures. The flowing ability, passing abil-
ity and the slump flow were assessed using the
L-Box, V-funnel and the slump flow apparatus.
The results obtained were compared with the
standards of EFNARC. The strength properties
were assessed using the compressive strength
and split tensile, this was done according to
ASTM C192 specifications.
Response surface methodology (RSM) was
adopted in the design of experimental combina-
tions. It also used to quantify the relationship be-
tween the controllable input parameters and the
obtained response surfaces.
Analysis of variance (ANOVA) was per-
formed for the data obtained in this experiment
for different replacement as the age increased.
The interaction between the input variables (ce-
ment, age and metakaolin) and the response of
different regression models developed for com-
pressive strength was investigated.
RESULTS AND DISCUSSION
Rheological properties of the fresh concrete
The segregation resistance of the self-
compacting concrete was determined by using
the V-funnel
test. According to EFNARC (2002) specifica-
tion the acceptable criteria for the V-funnel result
is between 6 and 12 seconds. On the basis of these
criteria, the SCC mix with metakaolin addition
from 15% and more did not satisfy this criterion
(Figure 1). This may be due to the fact that the
incorporation of high metakaolin content affected
the viscosity of the mix.

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Advances in Science and Technology Research Journal Vol. 13(2), 2019
L-box height ratios were measured and
the corresponding outcomes were presented in
Table 1. The result followed a similar trend with
the slump flow test. At 15% percentages and
greater addition of metakaolin, the L-box result
became unsatisfactory too, as seen in Figure 2.
The slump flow test was used to deter-
mine the ability of the SCC to flow in a non-
restricted condition. The factors affecting the
results of the T50
time are the amount, shape
and size distribution of aggregates and also the
viscosity and amount of paste, in accordance
with Uygunoglu and Topçu [2005]. The mix
with the lowest T50
time is the SCC with no
metakaolin addition (Table 1). On the basis of
the result, a direct relationship was established
with metakaolin quantity and T50
time based on
the EFNARC (2002) specification.
Strength properties
The result of the analysis showed that the ad-
dition of metakaolin to concrete resulted in an im-
proved strength till 10% replacement. Upon fur-
ther addition, the compressive strength began to
reduce. The highest strength across all ages was
recorded at 10% addition of metakaolin. How-
ever, at 15% and 20% (Figure 3) the strength was
still higher than the control. However, a decrease
in the compressive strength was noticed when
compared with 0% metakaolin at the percentages
higher than 20%.
The predicted R-Squared of 0.766 is in
reasonable agreement with the “Adjusted R-
Squared” of 0.809 as shown in Table 2. “Adeq
Precision” measures the signal to noise ratio. A
ratio greater than 4 is desirable. The model ratio
of 15.712 indicates an adequate signal. This mod-
el can be used to predict the effect of metakaolin,
cement and age on the compressive strength of
metakaolin concrete.
The model equation in terms of actual factor
is given in equation 1 as follows;
Compressive Strength = −184.70 + 1.60 A –
− 0.14 B + 813.61 C − 1.61 A2
+ 1.77 B2
−
−768.30 C2
+ 4.08 A·B – 3.19 A·C – 0.35 B·C
(1)
where: A – age,
B – metakaolin,
C – cement.
The results indicate that the addition of ce-
ment and metakaolin had a positive effect on the
strength properties of the developed self-com-
pacting concrete, as seen in equation 1.
The normal plot of residuals on the ex-
perimental run shows a close fit with the pre-
dicted values. Figure 4 shows no outlier in the
experimental runs.
The predictability plot of the model to account
for future occurences is as shown in Figure 4. The
predicted data points scatter round the actual data
points showing less overfitting and gave a pre-
dicted R-squared value of 0.767.
Synergetic effect of input parameters
on compressive strength
The Figures 5 and 6 show the contour plots
and 3D for determining the effects of Age and
Metakaolin against the compressive strength.
At low value of Metakaolin, the compressive
Figure 1. V-Funnel
Table 1. Slump flow
Metakaolin percentage
replacement T50
(Sec) Slump flow
0% (control mix) 3.5
5% replacement 4.0
10% replacement 4.4
15% replacement 5.6
20% replacement 7.3
25% replacement 8.1

4. Advances in Science and Technology Research Journal Vol. 13(2), 2019
10
strength increases as the Age of the concrete
grows from 3 to 150 days. This is in agree-
ment with the experimental results, as seen in
Figure 2.
From the numerical optimization obtained as
shown in the Figure 3, the maximum predicted
compressive strength of 44.35 N/mm2
was
achieved under the optimum concrete formation
of 110 days, Metakaolin of 52.73 kg. The desir-
ability of 1.00 was achieved with the numerical
optimization performed, showing best accuracy
of the developed model.
Figure 2. L-Box result
Figure 3. Compressive strength of dehydroxylated Kaolinitic clay versus age
Table 2. ANOVA for response surface quadratic model
Source
Sum of
Squares
DF
Mean
Square
F
Value
Prob > F
Model 2074.283 9 230.4759 26.00548 <0.0001 significant
A 623.8372 1 623.8372 70.38995 <0.0001
B 0.449426 1 0.449426 0.05071 0.8229
C 0.750283 1 0.750283 0.084657 0.7724
A2
472.1313 1 472.1313 53.27239 <0.0001
B2
0.008533 1 0.008533 0.000963 0.9754
C2
0.006395 1 0.006395 0.000722 0.9787
AB 38.7879 1 38.7879 4.376588 0.0422
AC 46.28101 1 46.28101 5.222064 0.0272
BC 0.000165 1 0.000165 1.86E-05 0.9966
Residual 389.9539 44 8.862589
Cor Total 2464.237 53

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Advances in Science and Technology Research Journal Vol. 13(2), 2019
Figure 4. Diagnostic plots of residuals and outlier against experimental runs
Figure 5. Contour Plots of the Response Surface

6. Advances in Science and Technology Research Journal Vol. 13(2), 2019
12
CONCLUSIONS
This research optimized the strength prop-
erties of metakaolin self-compacting concrete
using response surface methodology. This was
achieved using six concrete mixes by varying
the proportion of metakaolin at 0%, 5%, 10%,
15%, 20% and 25% respectively. The rheol-
ogy and strength properties of the developed
concrete were assessed at the fresh state and
hardened state respectively. The result of the
experimental analysis showed that the mix with
the lowest T50 time is the SCC with no metaka-
olin addition. Additionally, from the numerical
optimization obtained, the maximum predicted
compressive strength of 44.35 N/mm2
was ob-
tained under the optimum concrete formation of
110 days, Metakaolin of 52.73 kg. The age with
the optimum concrete strength formation is 110
days with metakaolin addition of 52.73 kg.
Acknowledgements
The authors are grateful to the manage-
ment of Covenant University, Ota Ogun State
and Nigeria Building and Road Research Insti-
tute, Ogun State for the previledge to use their
Structural labouratory.
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